The present invention relates to an apparatus for coating an areal substrate, and to methods of using the apparatus to coat substrates.
For over one hundred years the cathode ray tube has been the means of choice for the optical representation of still and/or moving pictures by means of raster-form spot representation. One disadvantage of the cathode ray tube, however, is that it has considerable depth such that, for example, flat television screens cannot be produced with it.
Therefore, for some time attempts have been to produce a flat screen or a flat display. Some of the best known of the structural elements developed over the last years and decades with which flat screens can be produced are light-emitting diodes (LEDs), liquid crystal elements (LCDs) and plasma elements. These modern structural elements, however, still have also specific disadvantages. Thus, conventional LEDs consume relatively significant levels of energy, while plasma elements, which are small fluorescent tubes, cannot be reduced to any desired size. The pixel raster of the plasma elements is limited to approximately 0.5 mm. More recent developments in the production of flat screens are directed toward so-called organic light-emitting diodes (OLEDs). The advantages of these organic light-emitting diodes comprises that at voltages of less than 5 volts they have low energy consumption, are strongly luminous, have a wide radiative angle, can be applied in temperature ranges from −40° C. to +85° C., and are of low weight. In addition, their quantum efficiency, i.e. the number of generated photons per injected electron or hole, has risen to more than 16% (Helmut Lemme: OLEDs—Senkrechtstarter aus Kunststoff, Elektronik 2/2000, p. 98, right column, paragraph 2, No. [5]: Yi He; Janicky, J.: High Efficiency Organic Polymer Light-Emitting Heterostructure Apparatuss, Eurodisplay '99, VDE-Verlag Berlin, Offenbach) and thus above the quantum efficiency of inorganic LEDs from III-V semiconductors. OLEDs thus are choices for applications in battery-operated apparatus. OLEDs are comprised of one or more semiconducting organic layers disposed between two electrodes with at least one of these electrodes, as a rule, being transparent. If an electric field is applied, electrons or holes are injected through the cathode or anode into the transport bands of the organic layer. Both charge carriers migrate toward one another and a certain portion of them recombines, whereby light quanta are generated through spontaneous emission (Helmuth Lemme: OLEDs—Senkrechtstarter aus Kunststoff, Elektronik 2/2000, pp. 97 to 103; E. Becker et al: Organische Lumineszenz: Neue Technologie für flache Bildschirme, Fernseh- und Kino-Technik, 8-9/2000, pp. 1 to 5).
The production of OLEDs can be accomplished by means of an OVPD (Organic Vapor Phase Deposition, U.S. Pat. No. 5,554,220) technology, in which a carrier gas stream at very low pressure in a heated reactor takes up materials and deposits these as thin layers on a substrate. This substrate can be, for example, an ITO (Indium Zinc Oxide) electrode which previously had been vapor-deposited onto glass. Onto the organic luminescent layer subsequently a further electrode is vapor-deposited and the electrodes with the active luminescent layer have approximately a thickness of 400 nanometers.
In a further method for the coating of a substrate with a thin organic layer, a substrate holder with a heater is provided, which holds on its underside a substrate, for example glass (EP 0 962 260 A1=U.S. Pat. No. 6,101,316). Beneath this substrate, two vaporizer sources are provided, which vaporize organic material which becomes deposited on the substrate if a diaphragm disposed between the substrate and the vaporizer is opened. With this method the uniform coating of substrates over large areas is not possible. Employing two separate vaporizers leads to superpositions of the vaporized materials on the substrate causing nonuniformity of the coating.
A vacuum vaporization installation is furthermore known, which comprises a vaporizer tank in which the material to be vaporized is vaporized. The topside of this vaporizer tank is provided with a hood extending outwardly in the horizontal direction (EP 0 477 474 A1). Linear distribution of the vaporized material is not attainable with this installation.
An apparatus is also known for coating a steel band, which comprises at least one vacuum vaporization container heated by induction. The apparatus is wherein each of the containers has an opening for the outlet of metal vapors and that the outlet opening for the metal vapors has the form of a narrow slot, disposed at a small spacing from the substrate to be coated (WO 96/35822). With this apparatus the linear distribution of vapor is also not possible.
A vaporizer source for the production of organic electroluminescence diodes is described in EP 0 982 411 A1. This source comprises a container of an insulating material, which receives the organic material. Closely around the container is placed a heater, which vaporizes the organic material. The container has a heating zone, which is heated directly by the heater and which is in contact with the organic material via a contact zone. The way in which the coating of substrates takes place is not described in detail.
In order to complete coatings over a large area, it is in principle possible to employ dot-form, line-form or areal vaporizers. While dot-form vaporizers are known for example through EP 0 982 411 A2 and EP 0 962 260 A1, a line-form vaporizer is already known from DE 42 04 938 C1. In the case of this line-form vaporizer, the vaporative deposition onto the substrate takes place from below. The same applies to a line-form vaporizer disclosed in DE 199 21 744 A1.
The disadvantage of dot-form vaporizers consists therein that with them a homogeneous coating on large areas can only be realized if the distance between vaporizer and substrate is large. This requires a coating installation to be very large in order for the distance between vaporizer and substrate to be large. In addition, only a small portion of the vaporizer material is utilized.
Moreover, the vaporizer source must be disposed beneath the substrate which can lead to problems with masks positioned between vaporizer source and substrate, and specifically not before the substrate reaches a size of approximately 300 mm×400 mm and with small structures in the masks.
If linear vaporizer sources are disposed horizontally and underneath a substrate to be coated, problems are encountered with masks starting at approximately 300 mm×400 mm and small structures within the masks, for example with pixel sizes from 0.4 mm×0.4 mm, since in this case the masks are sagging: which leads to inhomogeneous coating. In order to attain a high level of homogeneity with relatively thick layers, the vaporizer sources or the substrate must furthermore be moved slowly relative to one another.
The present invention provides an apparatus for the coating of substrates, which has a reduced space requirement, with which uniform coating can be achieved and with which it is also possible to apply large masks. Methods of using the apparatus to coat substrates are also a part of the invention.
The invention relates to an apparatus for coating an areal substrate, for example a rectangular plate. This apparatus comprises a vaporizer source and a distributor system for conveying vaporized material onto the substrate. The distributor system comprises a line source, with this line source and the substrate being movable relative to one another. The apparatus serves preferably for the production of flat screens with organic light-emitting diodes.
An advantage provided by the invention is that large quantities of areal material can be coated since the substrates are guided past a linear vaporizer source. Masks, disposed between vaporizer source and substrate, do not sag since they are disposed parallel to the areal substrate. In addition, efficient utilization of the vaporized material is made possible, and chemical reactions of vaporized organic materials with the surrounding parts do not take place. Furthermore, thereby that the entire distributor region beyond the crucible and before the final outlet opening is at a defined high temperature, condensation of the vaporized material is prevented without leading to a chemical decomposition of the organic molecules.
An embodiment example of the invention is depicted in the drawings and is described in further detail below.